1. Field of the Invention
The invention relates generally to controlled release formulations and more specifically to the use of hydrogels for delivery of therapeutic agents to subjects in need thereof.
2. Background Information
Hydrogels are materials that absorb solvents (such as water), undergo rapid swelling without discernible dissolution, and maintain three-dimensional networks capable of reversible deformation. Hydrogels may be uncrosslinked or crosslinked. Uncrosslinked hydrogels are able to absorb water but do not dissolve due to the presence of hydrophobic and hydrophilic regions. Covalently crosslinked networks of hydrophilic polymers, including water soluble polymers, are traditionally denoted as hydrogels when in the hydrated state. A number of aqueous hydrogels have been used in various biomedical applications, such as, for example, soft contact lenses, wound management, and drug delivery.
Hydrogels can be formed from natural polymers such as glycosaminoglycans and polysaccharides, proteins, etc., where the term “glycosaminoglycan” encompasses complex polysaccharides that are not biologically active (for example, not compounds such as ligands or proteins) and have repeating units of either the same saccharide subunit or two different saccharide subunits. The hydrogels most often cited in the literature are those made of water soluble polymers, such as polyvinyl pyrrolidone, which have been crosslinked with naturally derived biodegradable components such as those based on albumin. Another known substance for forming hydrogels, also known as a gelator, is amygdalin hydrogelators which are made by chemically modifying the naturally occurring glycoside amygdalin. Amygdalin may be found in apple, almond, peach, cherry and apricot pits and gels formed from these molecules are potentially toxic when degraded in the body. The production of amygdalin hydrogelators requires synthetic modification of the parent compound amygdalin to produce products capable of gelation.
Totally synthetic hydrogels that have been studied for controlled drug release, and as membranes for the treatment of post-surgical adhesion, are based on covalent networks formed by the addition polymerization of acrylic-terminated, water soluble chains of polyether dipolylactide block copolymers.
Many hydrogels are currently in use for drug delivery to a subject despite significant limitations, such as the need for chemical modification to produce substances suitable to form hydrogels and the inability of specific gelators to form hydrogels capable of incorporating therapeutic agents of widely varying solubility.